The present invention relates to video signal processing equipment. More particularly, the present invention relates to video data acquisition and display scan conversion apparatus and methods.
Television systems typically acquire picture data at high speed on a picture element (pixel) by pixel basis along a scanning line. Odd numbered lines are scanned as a first field, followed by the scanning of even lines of a second field. Adjacent odd and even fields have their lines "interlaced" in order to remove objectionably perceptible flicker from the display of the television video image. The use of interlaced fields provides for greater resolution in pictures having a high level of dynamic content (i.e. movement).
In some situations, particularly those characterized by low dynamic level, progressive scanning of the picture (i.e. the entire picture is scanned line after line in sequence) will yield greater picture detail in the vertical domain. The problem with the progressive scanning technique is that the flicker rate is one half that present with interlaced scan. With a typical field rate of thirty frames per second, progressive scan of all of the lines of each frame results in a flicker rate which is perceptible by the eye when displayed upon a viewing screen coated with phosphors having a normal persistence (e.g. P4 material). The flicker is subjectively displeasing to the viewer, and makes prolonged viewing difficult.
In the case of a picture image which is presented as the result of impulse illumination, such as an X-ray image excited by an X-ray burst from a pulsed X-ray tube which is displayed on the display screen of an image intensifier, it is known that the first field of an interlaced scan acquires more picture detail (energy) than is acquired by the second field. One explanation offered for this phenomenon is that the scan of the first field discharges adjacent pixels otherwise scanned in the second field. One solution to this problem has been to pulse the X-ray tube at the field rate (60 Hz) so that each field has been illuminated substantially equally. The significant drawback to this solution is that the subject, in many cases a human being undergoing medical imaging procedures, is thereby subjected to twice the amount of radiation.
A hitherto unsolved need has arisen for a video data acquisition and display system which optimizes the conditions for the acquisition of video data, and at the same time optimizes different conditions for the display of such data.
In some medical procedures, such as angioplasty, the physician feeds a cable through an artery into the heart cavity through valves. A radiopaque dye may be released into the bloodstream in the heart in order to locate the artery to which the cable is directed via X-ray imaging. The radiopaque die dissipates very rapidly, and the image outlining the artery system of the heart (called a "roadmap") is quite transitory. In the prior art disk recorder/players have been employed to capture and play back the road map. These machines have been expensive and have not been fully integrated with other related equipment. A hitherto unsolved need has arisen for a solid-state electronic video data acquisition and display system which effectively stores a roadmap image and recalls it for display at any time during the imaging operation.
A further hitherto unsolved need has arisen which enables video data in either progressive or interlace scan format to be converted to a high resolution interlace scan display format having at least 2n the number of original scanning lines, as well as a conventional scan format for storage; so that conventional video recording equipment may be used to store and playback the video data acquired by the system while at the same time enabling display of the video data at a higher resolution scanning rate than the rate employed during data acquisition.